This application claims priority under 35 USC xc2xa7119 of application number BO 2000A 000660, filed on Nov. 14, 2000 in Italy.
The present invention relates to a method of estimating the effect of the parasitic currents in an electromagnetic actuator for the control of an engine valve.
As is known, internal combustion engines of the type disclosed in Italian Patent Application BO99A000443 filed on Aug. 4, 1999 are currently being tested, in which the movement of the intake and exhaust valves is performed by electromagnetic actuators. These electromagnetic actuators have undoubted advantages since they make it possible to control each valve according to a law optimised with respect to any operating condition of the engine, whereas conventional mechanical actuators (typically camshafts) make it necessary to define a lift profile of the valves which is an acceptable compromise for all the possible operating conditions of the engine.
An electromagnetic actuator for a valve of an internal combustion engine of the type described above normally comprises at least one electromagnet adapted to displace an actuator body of ferromagnetic material mechanically connected to the stem of the respective valve. In order to apply a particular law of motion to the valve, a control unit drives the electromagnet with a current that varies over time in order appropriately to displace the actuator body.
It has been observed from experimental tests that in order to obtain a relatively high precision in the control of the valve it is necessary to control the position of the actuator body in feedback; it is therefore necessary to have a precise reading, substantially in real time, of the position of this actuator body.
In electromagnetic actuators of the type described above, the position of the actuator body is read by means of a laser sensor which is, however, costly, delicate and difficult to calibrate, and therefore unsuited to mass production. Methods have therefore been proposed for the estimation of the position of the actuator body based on the measurement of the electrical magnitudes (voltage and current) of the electrical circuits coupled to the actuating electromagnet.
These methods for estimating the position of the actuator body are not, however, very precise, as they are subject to the effect of the parasitic currents that are induced in the actuator body as a result of the rapid displacements of this actuator body.
In order to limit the effect of the parasitic currents induced in the actuator body, it has been proposed to make the actuator body from ferromagnetic, but not electrically conducting material, or it has been proposed to make the actuator body from laminated ferromagnetic material. It has been observed, however, that both when using a ferromagnetic but not electrically conducting material and when using a laminated ferromagnetic material, the effect of the parasitic currents induced in the actuator body is attenuated but not eliminated. Moreover, the use of a ferromagnetic but not electrically conducting material or a laminated ferromagnetic material reduces the mechanical strength of the actuator body.
The object of the present invention is to provide a method of estimating the effect of the parasitic currents in an electromagnetic actuator for the control of an engine valve that is free from the drawbacks described above and that is in particular simple and economic to embody.
The present invention therefore relates to a method of estimating the parasitic currents in an electromagnetic actuator for the control of an engine valve as claimed in claim 1.